Child abuse occurs at epidemic rates, with victims of abuse comprising a significant proportion of all child psychiatric admissions. Posttraumatic Stress Disorder (PTSD) is a common and often debilitating consequence of early child maltreatment, and currently little is known about the mechanisms that initiate and maintain the symptoms associated with this disorder. Emerging evidence in human and non-human primates suggest that the neurobiological changes associated with early stress may vary at different developmental periods. While much of the preclinical and clinical work on the effects of early stress point to the importance of the hippocampus as a key structure involved in the pathophysiology of PTSD in adults, recent findings suggest that alterations in the corpus callosum may be more prominent in juvenile samples. Consequently, in this study, assessments of the corpus callosum will be obtained using structural and diffusion tensor imaging in three groups of children: 50 maltreated children with PTSD, 50 trauma (e.g., maltreated) controls without psychopathology, and 50 normal controls with no lifetime history of intrafamilial or extrafamilial trauma and no lifetime history of psychopathology. Measures of inter-hemispheric transfer and memory function will also be obtained, together with comprehensive assessments of early trauma, social supports, current life stressors, and family loading for psychopathology. Neuroanatomical assessments will be obtained at baseline, and clinical and psychosocial assessments will be obtained at six-month intervals for two years after study intake. It is hypothesized that when compared to trauma and normal controls, maltreated children with PTSD will have reduced cross sectional area of the medial and caudal portions of the corpus callosum, and reduced fractional anisotropy in these regions (e.g., poorer integrity of white matter tracts). No changes in hippocampal volume are expected. A greater loading for anxiety and depressive disorders among first-degree relatives, an absence of positive stable supports, and exposure to ongoing stressors is expected to be associated with more severe PTSD symptomatology at intake, greater persistence of symptoms at follow-up, and more marked neuroimaging abnormalities.